FR2571357A1 - PROCESS FOR PREPARING SILICA TUBULAR GLASS - Google Patents

Abstract

PROCESS FOR PREPARING TUBULAR SILICA GLASS. IT CONSISTS OF ADDING ULTRAFINE PARTICLE SILICA TO THE SOLUTION OBTAINED BY HYDROLYZING THE METAL ALCOHOLATE IN A QUANTITY OF 0.2 TO 5 MOLES OF SILICA PER MOL OF METAL ALCOHOLATE; PLACING THE SOLUTION OF SOIL INCLUDING ULTRAFINE PARTICULATE SILICA IN A CYLINDRICAL CONTAINER AND GELIFYING THE SOLUTION BY ROTATING THE CONTAINER; DRY THE GEL TO FORM A DRY GEL; AND VITRIFY THE DRY GEL TO FORM A TUBULAR SILICA GLASS. APPLICATION TO OPTICAL FIBERS.

Description

257135?

  Process for the preparation of silica tubular glass

  The present invention relates to the sol-gel process for the preparation of silica glass using

  the solution obtained by adding ultra-fine particles

  silica to a hydrolysed solution of the alcohol

  metal, as a material, and more particularly

  the process of preparing a glass

  tubular silica by placing this solution of

  riau in a cylindrical container and gelling

  the material by rotating the container.

  As its purity improved, silica glass has recently become increasingly

  more widely used in various fields, such as

  set or the plate used to make

  semiconductor positive or central tube

  of the diffusion oven, proving its many

  its applications. In addition, silica glass is also used in glass equipment, such as test cups for chemical use, cells used for optical measurements. Its application as a substrate for thin film transistors (TFTs) draws particular attention and this is why it is expected that

  Silica glass is growing more and more.

  As mentioned above, the field of application

  silica glass is very large and the manufacturing process, quality and configuration of the

  Silica glass depend a lot on the use.

  Nowadays, as the new opti-

  transmission of information in the systems

  In order to transmit large amounts of information, optical fiber made of silica glass is used as the main material. In order to manufacture the master material for optical fibers, silica tubular glass is required as a starting material, but it is also needed to adjust the outer diameter of the finished fibers. Draconian requirements are imposed on the quality, as well as on the accuracy, of the dimensions of this silica tubular glass used as above, and this is why this tubular silica glass is very expensive, which is one of the most important problems for

  reduce the cost of optical fiber.

  Tubular glass manufacturing processes

  The commercially available silica are mainly the following three: 1) The natural quartz crystal is washed and etched. 2) SiO2 is obtained using SiCl4 or

  SiH4 of high purity as a material.

  3) We attack the natural silicon sand.

  The conventional processes as indicated above

  above have some disadvantages. Indeed, we can not use the third method as media

  optical communication because of its low pur-

  you. In all three processes mentioned above, it is necessary to carry out a treatment at a very high temperature. In addition, a common feature of these processes

  is that it is extremely difficult to ob-

  hold a round tubular silica glass.

  It has recently been attempted to manufacture silica tubular glass for an optical fiber by a

  process using the sol-gel process. Characteristics

  Distinctive features of the sol-gel process are that since the metal alcoholate is easily refined as a material, a high purity silica glass is obtained and the transparent silica glass is obtained at a temperature below the transition.

  For example, there is a procedure

  introduced by Hitachi, Ltd., according to which

  this material solution encompassing silicon alkoxide, water, alcohol and suitable solvent

  in the cylindrical container having a central bar

  the removable and gel material and before the contraction of the material begins, remove the central bar and dry the material and vitrify

  to obtain the tubular silica glass.

  But this process has the disadvantage that it is

  very difficult to obtain large glasses

  without cracks and therefore it is of course impossible to manufacture a long tube

silica glass.

  As another example, Ravinovich and his collaborators have made some attempts to manufacture silica tubular glass by the sol-gel process using the ultra-fine particle of silica as a material. This process is as follows: the ultrafine particle of silica is gelled and vitrified, then ground and redissolved to obtain the hydrosol solution; the hydrosol solution is placed in the cylindrical container in which the central bar is inserted; after having gelled the material, the central bar is extracted to obtain the tubular gel; drying and re-grinding the resulting gel yields silica tubular glass with an inside diameter of 1.7 cm, an outside diameter of

2.3 cm and a length of 25 cm.

  By this process, the production of rupturesor

  of splitting of the material in the process of

  dry gel and in the vitrification process is less frequent than in the other mentioned process.

  above. In addition, it is expected that this

  yielded a large tubular silica glass. But this

  yielded the disadvantage of implementing two stages of dispersion, of allowing a mixture of the impurities and of giving an optical quality of the

glass that is not uniform.

  As mentioned above, by the conventional sol-gel method, a tubular glass is not obtained.

  of silica which is satisfactory in terms of

quality sionset.

  The invention aims at applying the method introduced

  Japanese Patent Application No. 58/237577 by incorporating a new procedure into the sol-gel process and providing a tubular

  improved silica which is great and of a high quality.

  According to the invention, the tubular glass is prepared

silica gel as follows: -

  Water, hydrochloric acid and / or a solvent as needed are first added to a silicon alkoxide to effect hydrolysis to obtain the sol. Then, in the soil solution, are added ultra-fine particles of silica which is the white carbon commercially available under the names Cabocyle, Aerosil (produced by Degussa Co.), DC Silica (produced by Dow Corning Co.) Arc Silica (produced by PPG Co.), etc., and the solution stirred well. The resulting soil is placed in a cylindrical vessel of a hydrophobic material such as polypropylene, polyvinyl chloride, polyfluoride of ethylene, glass, etc. The material is gelled by rotating the container under the effect of a rotating machine and dried in dry gel. The dry gel is gradually heated from room temperature to a temperature determined at

  in advance and is maintained at this temperature

  given in advance to eliminate the

  pores in order to obtain the tubular silica glass.

  Following the process above, in comparison

  with the process in which we do not add the parti-

  ultra-fine silica, the cracking of the gel at

  drying time is less likely to occur

  reduce. In addition, as the dry gel obtained according to

  vention is porous, rupture and splitting

  vitrification are also lower. In-

  the tubular form of the gel is obtained by using

  the centrifugal force, so that the surface

  the tube is a clean and smooth surface. Consequently, if the accuracy of the rotating machine and the cylindrical container is sufficient, it is very easy to obtain a tubular glass in

  very round silica and a large size.

  There are two reasons why a large silica glass, including a tubular glass, can not be obtained by the conventional sol-gel process. When making the gel dry, the drying of the gel is accompanied by a

  contraction of the gel and when vitrified, it appears

  there is a phenomenon of foaming which both make

  cracking most likely occurs.

  Following the study of Nogami and his collaborators

  In the sol-gel process using the metal alcoholate as a material, it is possible to prevent the appearance of splitting at the time of vitrification.

  porous dry gel having a large number of pores relative to

o

  from 50 to 100 A (5 to 10 m). This is corro-

  It is also recognized by the fact that the dry gel obtained in the Ravinovich et al. solgel method using ultrafine silica particles is unlikely to crack because the dry gel obtained by hydrolysing the metal alcoholate with ammonia (this dry gel is much more porous than that obtained by hydrolyzing with acid) is

much more free of cracking.

  According to the method of the invention, by adding the ultra-fine particles of silica to the soil obtained by hydrolysing the metal alkoxide, the dry gel obtained

  is porous, which decreases the appearance of

  at the time of vitrification. In addition, as there is

  very little foam in the silica glass after vitri-

  the optical characteristics of the glass of

silica are excellent.

  Like what is required of the ultraparticle

  The fine silica used according to the invention is

  mentally only to have an effect that makes the gel porous dry, the silica that can be used

  is not limited to the white carbon mentioned above.

  such as Aerosil and Kyabocyl obtained in hydro-

  lysing SiC14 by the oxyhydrogen torch such

  than previously mentioned, but silica in particular

  ultra-fine particle obtained by the wet process in use

  Reading sodium silicon is also applicable.

  It is well known that by hydrolyzing alcohol

  metal by ammonia, silica is produced in fine particles. By collecting the silica in fine particles, silica is obtained in ultrafine particles which is very similar to

  white carbon mentioned above. This silica,

  Ultra-fine particles also have the same effect.

  In studies carried out on the process to prevent the cracking of dry gel, it has been found that

  the resistance of the gel to a great contraction at

  drying depends a lot on the pH of the gel. The pH of the sol obtained by hydrolyzing the metal alkoxide with an acid catalyst is from 1 to about 2. If a base such as ammonia is added to this soil to increase the pH value, the rate of setting

  in gel increases and the gel structure becomes sufficiently

  Strongly strong to withstand the great contraction at the time of drying. In particular, when the pH is between 3 and 6 the gel, which is very strong, is

unlikely to crack.

  That's why glass is made

  tubular silica by the process according to the invention

  Silica tubular glass can be obtained by adjusting the pH of the soil and by gelling

  the soil while rotating the container.

  As a basis for adjusting the pH of the soil, use may be made of ammonia, ammonia, an aqueous ammonia solution, an organic base such as triethylamine, an aqueous triethylamine solution, pyridine, an aqueous solution of pyridine, aniline and an aqueous solution of aniline, etc. But bases comprising an alkali metal ion, such as sodium hydroxide, potassium hydroxide, etc., are not desirable for producing silica glass, because the positive ions remain in

  the silica glass obtained. Nevertheless, these bases include

  the alkali metal ions are effective for

  multi-constituent glass such as

sodium glass.

  We will explain below how to perform the

  rotation to gel the soil when one turns

the container.

  According to the method of the invention, as

  above, such as ultrafine silica

  fines is suspended in the liquid phase mainly comprising ethyl silicate, the particles-finite silica deposits under the effect of centrifugal force due to rotation, which renders the composition of the soil non-uniform and, consequently, gel. This lack of uniformity of

  composition of the gel causes not only the cracking

  at the time of drying or vitrification, but also

  deterioration of the optical characteristics of the material. That's why the number and duration

  rotations for gelling should be

  in the range in which there is no suspension of silica in fine particles

  the material constituting the soil. The parameters governing

  The suspension of the silica in fine particles is, by giving the size of the tubular silica glass obtained, the rotation speed, the rotation time and the composition of the constituent material.

  the soil at the time of gelation by rotation.

  Of the three parameters above, the duration of rotation

  tation is determined mainly by the relation between the gel time and the dry gel yield and the composition of the material constituting

  the soil is best defined according to the conditions

  subsequent vitrification. So we have to adjust the -

  suspension of silica into fine particles mainly

  by the number of turns. Centric acceleration

  minimal effect acting on the silica in fine parti-

  cules of the material constituting the soil, in the reci-

  The maximum weight of the rotating needle is lg (980 cm / second2), but its maximum varies according to the particle diameter of the silica in fine particles and the

  distance between the silica and the axis of the cylindrical container

  turning, the number of turns is not defined.

  Nevertheless, for example in the case in which the

  particle diameter of silica in fine particles

  The capsules used are approximately 500 A (50 m "), and the diameter of the rotating container is 5 cm, when the silica in

  fine particles in the vicinity of the circumference

  the outermost part of the container is exposed

  a force of gravity of 500g for more than 30 minutes

  the suspension of the silica is considered

  maple. In the case where the material is the soil solution which does not include silica in fine particles,

  if the soil is subjected to a higher gravitational force

  at 1000 g, cracking takes place at the time of gelling. That's why we make the assumption

  that the number of laps must be included in the

  for which the gravitational force to which the soil solution is subjected does not exceed 10009o

  When a large dry gel is produced

  the yield is lowered if the container and the drying conditions are not adequate. The following is an explanation of the container and drying conditions which are suitable for improving

the yield.

  The container for the gel, used when producing the dry gel, is advantageously made of a material

  hydrophobic. When the gel is dried, the gel contracts

  For example, 70% of its initial size should be so that the material of the container should be such that the affinity between the gel and the container is low and the gel slides easily on the inner surface of the container. For example, organic polymers are very suitable for

  such as polypropylene, poly (ethyl fluoride)

  lene), polyvinyl chloride, polyethylene, polystyrene, etc. The coating formed by depositing

  organic polymers as above in the above-mentioned

  face of a mineral material such as glass, is also suitable. It goes without saying that the rotating container that meets the above requirements can be used

  as a container for the next drying process.

  The drying conditions depend on the rate of evaporation of the solvent, such as water and the alcohol included in the gel. That's why we make

  optimal conditions according to the rate of opening

  container cover (total area of the

  lid openings in relation to the total area

  lid), drying temperature and humidity.

  If the opening rate of the lid of the

  decreases and the rate of evaporation of soil

  As the gel is lowered, it is unlikely that the gel will crack. But if we extend the time required for manufacturing, we increase the

  manufacturing cost. We must therefore seek a compromise

  shortened the duration of production and improved

product performance.

  In addition, the probability of the cracking of the gel depends on the drying temperature, that is to say that the gel is all the stronger as the temperature is higher, which improves the yield. But if the drying temperature is higher than the boiling point of the solvent, it becomes difficult to

  make master of the drying speed. It's for-

  what the drying temperature should be at most C. Experiments carried out bearing in mind

  The above shows that the optimum conditions

  the drying is that the drying temperature is between ambient temperature (20 C) and 120 C and that the opening rate of the lid of the container is 50%, or less than this value,

  and preferably 10% or less of this value.

  After gelation, the gel is heated to

  drying temperature determined in advance to ob-

  keep the gel dry. At this moment, the speed of heating

  fage should be as low as possible to obtain a good yield. But, in order to reduce the time required for manufacture, it is desirable that the speed of

  heating is as high as possible. Considering

  of the foregoing, the appropriate heating rate is 120 C / hour, or is a speed

less than this value.

  The following explains the conditions of pro-

  duction of dry gel. Then we describe the vitri-

  giving an improvement in the performance and

the quality of the products.

  Vitrification consists of the following three stages:

  1) removal of absorbed water, 2) carbon removal,

3) make the gel dry non-porous.

  Of the three stages mentioned above,

  the stage 1) of elimination of the water absorbed at the in-

  the greatest influence on performance at the moment of vitri-

  fication. In the dry gel, there is a large amount

  physically absorbed water that can be removed

  born by the heat treatment at 4000 C approximately. But if the absorbed water is abruptly removed by rapidly heating the gel, the cracking of the gel often occurs, which decreases the yield. If we decrease

  the heating rate, the efficiency is well

  but the cost of manufacture increases. The experiences

  According to the invention, it has been shown that the upper limit of the heating rate, which allows

  eliminate absorbed water without lowering the efficiency

  400 C / hour, and that the gel must be

  kept at a temperature chosen between the temperature

  room temperature (20 C) and 400 C for one hour and

more, at least once.

  In stage 2), the carbon is removed by the heat treatment at a temperature between

  400 and 1100 C. The heating rate of this treatment

  temperature also affects performance, although it is not as large as in the

  stage 1), to remove the absorbed water. Experiences

  these showed that the heating rate which con-

  comes the best is between 30 and 400 C to

  time and that the freeze should be maintained at a

  selected in the range mentioned above for at least 3 hours, at least once. If the

  pH was adjusted by the addition of a base, as de-

  previously written, the hydrochloride of the base remains in the dry gel. But the hydrochloride decomposes with the carbon products in stage 2), to eliminate

  carbon products, which is very advantageous.

  In stage 3), the non-porous dry gel is made by a heat treatment at a temperature of between about 1000 and 1400 C, although the temperature range varies according to the concentration of the

  silica in ultra-fine particles. The speed of heating

  appropriate age, to raise the temperature of the

  elimination temperature of carDone from stage 2 to temperature

  ratude rendering the gel non-porous dry is between 30 and 4000 C per hour. By keeping the gel dry at the temperature that makes it non-porous during the

  fixed period in advance, we obtain a trans-

  Silicon glass in the absorption spectrum of near infrared radiation, Vickers hardness, density and other properties which are generally equivalent to those of silica glass

classic.

  However, in the process as indicated above

  above, if the silica glass is kept

  for a long time at a temperature above

  In order to render the gel non-porous, after completion of step 3), the foam tends to occur in the glass. The aspect of this foaming phenomenon depends on

  the water content of the silica glass after removal

  pore. Indeed, the foaming will occur especially as the water content of the silica glass is smaller. The water content in turn depends

  of the concentration of silica into ultraviolet particles

  fines. Foaming will be less frequent as the concentration of silica is greater. That's why, in order to prevent foaming, it is good

  to increase the concentration of the silica in particular

  the ultra-fine to add, although> if the concentration

If the silica is too large, the production yield of the dry gel decreases. It follows that the appropriate concentration of silica in ultra-fine particles, which decreases the tendency of the foaming to occur without reducing the yield, is between 0.2 and 5 moles per mole of metal alcoholate

  (i.e. metal alkoxide: silica in particular

ultra-fine = 1: 0.2 to 5).

  Sometimes crystals such as cristbalite and trydimite are produced in the silica glass after vitrification, which is a kind of devitrification phenomenon. It has now been found that this phenomenon of devitrification occurs more often when the silica in ultra-fine particles - is not dispersed uniformly in the soil, or when the soil comprises a small amount of impurities. For

  to improve the dispersibility of the silica in particular

  ultra-fine, the application of ultrasonic vibrations

  ground sound or centrifugal separation are very

2 5 7 1357

  effective. In particular, it has been shown, according to

  vention, that the centrifugal separation eliminates the

  impurities, which is extremely effective in preventing

dear devitrification.

  The following examples illustrate the invention.

Example 1

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  commercially available and the mixture is stirred violently for hydrolysis. Then 216 g of silica in ultra-fine particles ("Cabosil" having a specific surface area of 200 m 2 / g) are added to the solution obtained.

  while stirring and adding, in addition, ammonia

  than normal 0.1 drip to adjust the pH of

the solution at 4.5.

  1256 ml of the soil solution are placed in the cylindrical rotating vinyl chloride vessel whose internal diameter and length are 5 cm and 100 cm respectively, and both of which

  ends are closed by rubber stoppers.

  Then the container is fixed in the rotating machine shown in Figure 1 and rotated at 2000rpm. In Figure 1, 1 is the container, 2 is a motor, 3 is a shaft bearing, 4 is a

  fixing element for fixing the container

  being the motor and the bearing 3, 5 is a guide rail

  age to fix the motor 2 and the bearing 3 and 6 is a

  support plate. 50 minutes after the start of

  After confirming with a sample that the gel setting has been completed, the container of the rotating machine is removed and left overnight.

  The gel obtained is placed in a box of poly-

  propylene whose dimensions are 50 cm in width, 120 cm in length and 20 cm in height, and the material is heated from 20 C to 60 C, at a speed of

  heating of 2 C / hour. The gel is dried at 60 ° C.

  7 days to obtain the dry gel with

  3 cm in outside diameter, 2 cm in diameter,

  meter and 60 cm in length, this gel being stable enough that it does not occur cracking, even when maintained at room temperature. Two of the 20 dry gels prepared under the same conditions crack and 18 are

  good, giving a 90% return.

  The 18 dry gels are put in the vitreous oven.

  and heat them from room temperature

  at 200 C, at a heating rate of 60 C / hour.

  The materials are then maintained at 60 ° C for one hour to remove the absorbed water. The obtained materials are heated to 950.degree. C. at a speed of 180.degree.

  temperature at which the materials are kept

  18 hours to remove carbon and ammonium chloride. The temperature is raised to 1200 ° C. at a heating rate of 180 ° C./hour and the gel is kept dry at this temperature for 1.5 hours so that it is not porous and transparent tubular silica glass is obtained ( with an outer diameter of 2.5 cm, an internal diameter of 1.5 cm and a

  length of 50 cm). In the process of vitrification men-

  tioned above, there is no gel in which a

  cracking occurs and all 18 tubular glasses

  Silica resins are intact, resulting in

100%.

Example 2

  840 ml 0.01 N hydrochloric acid is added to 624 g of commercially available refined silicon ethoxide and the solution is violently shaken to effect hydrolysis. To the solution obtained, 77.4 g of ultra-fine fumed silica ("Nipsil" E220A) having a particle diameter of 1.5 microns obtained by the wet process were added using the sodium silicate produced by Nihon Silica. Kogyo

  Co., Ltd., as a material, while stirring, and ultrasonic vibration was applied to the soil. We adjust the

  pH of the soil at 4.5 by adding dropwise ammonia

normal 0.1 niac.

  1256 ml of the soil solution obtained in the cylindrical vessel rotating with

  vinyl, the dimensions of which are of an inte-

  5 cm and a length of 100 cm and both ends of which are closed by

  The container is fixed in the machine

  as shown in FIG. 1, and is rotated at a speed of 1500 revolutions / minute. It is rotated for 60 minutes then, after confirmation that the gel setting is completed by a sample, the container is removed from the rotating machine and

leave it overnight.

  The gel obtained is placed in a box of poly-

  propylene 50 cm wide, 120 cm long

  and 20 cm in height with a lid whose

  vertures represent 0.8% of the surface and

  heats the gel from 20 C to 70 C at a heating rate

  fage of 2 C / hour. After drying the gel at 70 ° C for 12 days, a dry gel (2.5 cm outer diameter, 1.5 cm inner diameter and 50 cm length) is obtained, which is stable enough that there is no cracking, even if it is kept at room temperature. Three of the 20 dry gels produced under the same conditions

  are cracking and 17 are good, so that the

is 85%.

  The 17 dry gels thus obtained are placed in

  the vitrification oven and they are heated by the temperature

  Ambient temperature at 300 C at the heating rate of C / hour and held at this temperature for 2 hours to remove the absorbed water. We

  heat the dry gels to 950 C,

  They are heated at 180 ° C / hour and kept at this temperature for 18 hours to remove carbon and ammonium chloride. The temperature is then raised to 1120 ° C. at a rate of 180 ° C./hour and the dry gels are kept at 1120 ° C. for 1.5 hours so that they are not porous, and the tubular transparent silica glass is then obtained. an outside diameter of 2.1 cm, an inside diameter

  of 1.3 cm and a length of 43 cm. In the vitreo-

  mentioned above, 2 dry gels were

  dare and we get 15 tubular silica glasses

  intact ,. the yield thus being 88.2%.

Example 3

  840 ml 0.01 N hydrochloric acid is added to 624 g of commercially available refined silicon ethoxide and the solution is violently shaken to effect hydrolysis. Independently, a mixed solution of 14 ml of 28% ammonia, liters of ethanol and 200 ml of water is added to the mixed solution of 800 ml of silicon ethoxide and 3.4 liters of ethanol. , and the resulting solution is stirred

Room temperature.

  After keeping the solution overnight, the silica is recovered in ultra-fine particles by thickening under reduced pressure. It is dried at 200 ° C. overnight and under a stream of air and

  of nitrogen the silica into ultrafine particles recovered

  SOE. 180 g of this silica in ultra-fine particles are added to the hydrolysed solution above, while stirring, and an ultrasonic vibration is applied.

  to obtain a soil in which the silica is dispersed

  in a uniform manner. We add drop by drop

  soil ammonia, 0.1N to adjust the pH to 4.5.

  1256 ml of the soil solution are poured into

  the cylindrical container turning into vinychloride

  It is 5 cm inside diameter and 100 cm long, both ends of which are closed by rubber stoppers. We fix the container in

  the rotating machine, as shown in FIG.

  re 1, and rotated at 500 rpm.

  After running it for 30 minutes, and

  after confirming that the gel setting of a sample

  lon is completed, remove the container from the machine

  rotating and we abandon it for one night.

  The obtained gel is put in a box (width of 50 cm, length 120 cm and height 20 cm) made of polypropylene having a lid whose openings represent 1.0% of the surface and heating of

  CPU at 60 c, at the heating rate of 2 C / hour.

  After having dried the gel at 60 C for 7 days,

  gets the dry gel (outer diameter 3.5 cm, dia-

  inner meter of 2.1 cm and length of 70 cm) which is stable enough for it not to occur

  no cracking, even at room temperature.

  3 of the 20 dry gels formed under the same conditions crack and 7 are good, the yield being thus

85%.

  17 dry gels are placed in the vitreous oven

  and heated from room temperature to C at the heating rate of 60 C / hour, and

  keeps them at this temperature for 3 hours.

  The temperature is raised to 300 ° C. at a rate of C / hour and the dry gels are kept at 300 ° C. for 5 hours to remove the absorbed water. The dry gels were further heated to 950 ° C at 180 ° C / hour and held at 950 ° C for 18 hours to remove carbon and ammonium chloride. Then the temperature is raised to 1220WC at a speed of 180O C / hour and, after having been maintained at this temperature for 1.5 hours, the dry gels become non-porous and

  transparent tubular silica glass (outer diameter

  2.4 cm inside diameter, 1.4 cm inside diameter and

  47 cm). During the vitrification process, dry gels crack and 12 silica glasses are obtained which are good, giving a yield of 70.6%. There is no tubular silica glass that exhibits devitrification or

  Foaming and the quality is excellent.

Example 4

  840 ml of 0.01N hydrochloric acid are added to 456 g of the refined silicon methoxide and shaken.

  violently the solution to perform the hydrolysis.

  270 g of the ultrafine particulate

  fine ("Aerosil" with a specific surface area of 50 m2 / g). To the solution, while agitating, one applies an ultrasonic vibration. The masses are removed by centrifugal separation to obtain a sol in which the silica is dispersed in a uniform manner. Normal 0.1 ammonia is added dropwise to the soil

obtained to adjust the pH to 4.5.

  1256 ml of the soil obtained is poured into the

  Cylindrical dough rotating in vinyl chloride of inner diameter cm and 100 cm in length and the two ends of the containers are closed by rubber plugs. The container is fixed in the rotating machine as shown in Figure 1 and rotated at 1000 rpm. After having

  run for 30 minutes and after confirming

  When the sample is completely set in gel, remove the container from the rotating machine and

leave it overnight.

  The gel obtained in the box (width 50 cm, length 120 cm and height 20 cm) is placed in polypropylene having a lid whose openings represent 0.8% of the surface. The gel is heated from 20 ° C. to 70 ° C. at a heating rate of 5 ° C./hour and, after drying the gel at 70 ° C. for 7 days, a dry gel (3.5 cm outside diameter, 2.1 cm inside diameter and 70 cm in length) which is stable enough that it does not occur

  no cracking, even at room temperature.

  Dry gels formed under the same conditions are intact and there is no cracking, the yield

therefore being 100%.

  We place 20 dry gels formed as above

  in the vitrification oven and heat them with the

  room temperature at 200 C, at the heating rate of 60 C / hour. After maintaining the dry gels at

  this temperature for 3 hours, the temperature is

  at 300 C, at a rate of 60 C / hour, and the material is maintained at 300 C for 5 hours to remove the absorbed water. The dry gels are further heated to 950 ° C. at the heating rate of

   C / hour and held for eighteen hours

  to remove carbon and ammonium chloride.

  The dry gels obtained at a speed of 180 C / hour are heated further to 1230 C and maintained therein.

  for an hour to make them non-porous. We ob-

  then holds transparent tubular silica glass (outer diameter of 2.5 cm, internal diameter of 1.6 cm and length of 52 cm). During the vitrification process, no dry gel breaks and 20 intact tubular glasses of silica are obtained.

  yield is therefore 100%. In addition, it does not

  no devitrification or foaming in any

  silica glasses and the quality is excellent.

Example 5

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  in commerce, and the solution is violently

  to perform the hydrolysis. We add to the solution

  219 g of silica in ultrafine particles ("Aerosil OX50" with a specific surface area

  is 50 m2 / g) and an ultrasonic vibration is applied.

  sound. Then the mass-forming substances are removed by centrifugal separation to obtain the soil in

  wherein the silica is dispersed in a uniform manner.

  The pH of the soil is adjusted to 4.5 by adding an ethanolic solution of triethylamine at the concentration of

0.1 mole / liter.

  1256 ml of the sol solution obtained is poured into the rotating cylindrical vinyl chloride vessel 5 cm inside diameter and 100 cm in length, the two ends of which are closed by rubber plugs.

  the rotating machine as shown in FIG.

  re 1 and rotated at 500 rpm. After having run for 30 minutes and having confirmed that the freezing of the sample has been completed, the container of the rotating machine is removed and it is abandoned.

for one night.

  The gel obtained in the box (50 cm wide, 120 cm long and 20 cm high) is placed in polypropylene having a lid whose

  openings represent 1.0% of the area. We heat

  the gel at 40 ° C. at 70 ° C., at a heating rate of 5 ° C./hour and drying the gel at 70 ° C. for 7 days, the dry gel is obtained (outside diameter 3.5 cm, inside diameter 2 , 1 cm and length 70 cm) which is sufficiently stable so that cracking does not occur even at room temperature. 2 of the 20 dry gels formed under the same conditions crack and 18 dry gels are obtained

  intact, the yield being thus 90%.

  We put the 18 dry gels above in the

  vitrification oven and heat them up

  ambient temperature at 200 C at the heating rate of C / hour. After keeping the dry gels at C for 3 hours, the temperature was raised to 300 C at a rate of 60 C / hour and the dry gels were kept at 300 C for 5 hours to remove the absorbed water. The dry gels are then heated further to 900 ° C. at a rate of 180 ° C./hour and held there for 9 hours to remove the carbon and the hydrochlorides bring the material to 1220 ° C. at a rate of 180 ° C./hr. the material at this temperature for 1.5 hours to obtain non-porous and transparent silica glass (outer diameter of 2.5 cm, inner diameter of 1.5 cm and

  length of 50 cm). During the vitrification process

  cation, no dry gel cracked and 18 glasses of silica are obtained intact, the yield is therefore 100%. In addition, there is no devitrification or foaming and the quality of the silica glass is

excellent.

Example 6

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  in commerce, and the solution is violently

  to perform the hydrolysis. 219 g of silica are added to ultrafine particles ("Aerosil OX50"

  with a specific surface area of 50 m2 / g)

  obtained while stirring and apply the vibra-

  ultrasound The mass-forming substances are removed by centrifugal separation to obtain the sol in which the silica is dispersed in a uniform manner. Then, to adjust the pH to 4.5 is added, drop by drop, an ethanolic solution of pyridine

  at a concentration of 0.1 mole / liter.

  1256 ml of the soil solution obtained is poured into the rotating cylindrical vessel (inner diameter of 5 cm, length 100 cm) into Teflon and the two ends of the vessel are closed by rubber stoppers. The vessel is placed on the rotating machine as shown in FIG. 1 and rotated at 1500 rpm. After

  have been running for 30 minutes and having

  that the sample is completely gelled, remove the container from the rotating machine and

leave it overnight.

  The gel obtained in the box (cm in width, 120 cm in length and 20 cm in height) is placed in polypropylene having a lid whose openings represent 1.0% of the surface and is heated from 5 to 60 C at the heating rate of C / hour. By drying the gel at 60 ° C. for 7 days, the dry gel (with an external diameter of 3.5 cm, an internal diameter of 2.1 cm and a length of 70 cm) is obtained which is sufficiently stable so that cracking does not occur even at room temperature. 3 of the 20 dry gels formed under the same conditions crack and 17 intact dry gels are obtained, the yield thus being%. We put the 17 dry gels above in the

  vitrification oven and they are heated from the

  ambient temperature at 200 C at the heating rate of C / hour, at which temperature the gels are kept dry for 3 hours. The material is heated to 300 ° C. at a heating rate of 60 ° C./hour and kept there for 5 hours to remove the absorbed water. The material is then further heated to 900 ° C at a rate of 180 ° C / hour and maintained at 900 ° C for 9 hours to remove carbon and hydrochloride. The temperature is further raised to 1220 ° C. at a rate of 180 ° C./hour and the material is maintained at 12 ° C. for 1.5 hours so that it becomes non-porous and the transparent silica-glass tubular (outer diameter of 2.5 cm, internal diameter of

  1.5 cm and length of 50 cm). In the vitreo-

  As a result, no dry gel cracked and 17 intact silica glasses were obtained, thus yielding 100%. In addition, there is no devitrification or foaming and the quality of the glasses obtained is excellent.

Example 7

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  commercially available and the solution is violently shaken to effect hydrolysis. To the solution obtained is added, with stirring, 180 g of silica in ultrafine particles ("Cabosil" whose surface

  specific is 200 m 2 / g) and a vibratory

  ultrasound The substances forming

  mass by a centrifugal separation so as to dis-

  to penetrate the silica evenly in the soil.

  Then we adjust the pH of the soil by bubbling with

  ammonia diluted in nitrogen gas.

  1256 ml of the soil solution obtained is

  in the rotating cylindrical container (5 cm internal diameter and 100 cm long) made of vinyl chloride, both ends of which are closed by rubber stoppers. The container is fixed on the rotating machine as shown

  in Figure 1 and rotated at 1000 rpm.

  After running for 50 minutes and

  after confirming that the sample is

  taken in gel, remove the container from the

  China turns and is abandoned for one night. The resulting gel is placed in the box (cm in width, 120 cm in length and 20 cm in height) made of polypropylene having a lid whose openings represent 5.0% of the surface and is raised from 30 C to 60 C at the heating rate of C /: hour. By drying the gel at 60 ° C. for 7 days, a dry gel (with an outside diameter of 2.9 cm, an internal diameter of 1.9 cm and a length of 58 cm) is obtained which is sufficiently stable so that cracking does not occur even at room temperature. 5 of the 20 dry gels formed under the same conditions crack and dry gels are obtained, the yield thus being%.

  The dry gels mentioned below are placed

  top in the vitrification oven and one wears them from the

  room temperature at 200 C, at the heating rate

  fage of 60 C / hour. After keeping the gels dry at 200 ° C. for 3 hours, the materials are heated to 300 ° C. at a heating rate of 60 ° C./ hour and

  they are kept at 300 C for 5 hours to elimi-

  destroy the absorbed water. Dry gels are still heated

  at 950 C at a speed of 180 C / hour and are

  hold at 950 C for 18 hours to eliminate the car-

  bone and ammonium chloride. The temperature is further raised to 1220 ° C. at a rate of 180 ° C./hour and the material is maintained at 12 ° C. for 1.5 hours to make it non-porous and the glass is obtained.

  tubular transparent silica (of an outside diameter

  2.4 cm, with an inside diameter of 1.5 cm and

  of a length of 47 cm). No dry gel is cracking

  in the vitrification process and intact silica tubular glasses are obtained, the yield thus being 100%. In addition, there is no devitrification or foaming and the quality of

  Silica glasses obtained is excellent.

Example 8

  540 ml of normal 0.02 g hydrochloric acid is added to 624 g of the commercially available refined silicon ethoxide and the solution is violently shaken to effect hydrolysis. 300 ml of water are added to the solution obtained, then g of silica in ultrafine particles ("Aerosil OX50" with a specific surface area of 50 m 2 / g) is added while stirring. The silica is uniformly dispersed in the soil by ultrasonic vibration. The pH of the

sol obtained is 2.15.

  1256 ml of the soil solution obtained is

  in the rotating cylindrical container (with an inside diameter of 5 cm and a length of

  cm) of vinyl chloride, both of which

  trenches are closed by rubber stoppers

  Chouc. The container is fixed on the rotating machine as shown in FIG. 1 and rotated at 2000 rpm. After having run for a few minutes, and having confirmed that the sample is completely set in gel, the container is removed and

we leave it overnight.

  The gel obtained in the box (50 cm wide, 120 cm long and 20 cm high) is made of polypropylene having a lid whose openings represent 0.1% of the surface and the gel is brought from 20 C to 60 C at the heating rate of 2 C / hour. Drying the gel at 60 ° C. for 15 days gives a dry gel (3.5 cm outside diameter,

  2.1 cm inside diameter and 70 cm

  which is stable enough that no

  not occur even at room temperature.

  ature. 8 of the 20 dry gels formed in the same way

  ditions crack and 12 dry gels are obtained

  intact, the yield being thus 60%.

  The above 12 dry gels are placed in the vitrification oven and are brought from room temperature to 200 ° C. at a heating rate of 60 ° C./hour. After keeping them at 200 ° C. for 3 hours, the material is further heated to 300 ° C. at a heating rate of 60 ° C./hour and is maintained.

  at 300 C for 5 hours to remove the absorbed water.

  Then we bring the material-at 950 C at the speed of

  180 C / hour and maintained at 950 C for 3 hours

  to remove carbon. We raise the temperature

  at 1200 C at a speed of 180 C / hour and it is

  holds at 12000 C for 1.5 hours to make it no

  porous and we then obtain the trans-

  Silica parent (2.4 cm outside diameter, 1.4 cm inside diameter and 47 cm long). In the vitrification process, no dry gel splits and 12 intact silica tubular glasses are obtained, the yield being

  so 100%. Moreover, there is no devitrifica-

  neither foaming nor the quality of silica glasses

obtained is excellent.

Example 9

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  in commerce and the solution is violently

  to perform the hydrolysis. We add to the solution

  210 g of the ultrafine silica ("Aerosil OX50" with a specific surface area of 50 m 2 / g) are obtained and stirred, and the ultrasonic vibration is applied. Mass-forming substances are removed by centrifugal separation to obtain the soil

  wherein the silica is dispersed uniformly.

  Then, 0.1 normal ammonia is added dropwise to the soil to adjust the pH to 4.5.

* 1256 ml of the soil solution obtained is

  in the rotating cylindrical container (with an inside diameter of 5 cm and a length of

  cm) of vinyl chloride, both of which

  are closed by rubber stoppers. The container is fixed on the rotating machine, as shown in FIG. 1, and is rotated at 1500 rpm. After spinning for 30

  minutes and confirm that the sample is

  taken in gel, remove the container from the

  rotating machine and we abandon it for one night.

  The gel obtained in the box (50 cm in width, 120 cm in length and 20 cm in height) is made of polypropylene having a lid whose openings represent 1.0% of the surface and is brought to 20 C at 60 C at the heating rate of 2 C / hour. Drying the gel at 60 ° C for 7 days yields a dry gel (3.5 cm outer diameter, 2.1 cm inner diameter and 70 cm long) which is stable enough to not occur.

  no cracking, even at room temperature.

  One of the 20 dry gels formed under the same conditions cracks and 19 intact dry gels are obtained,

the yield is thus 95%.

  The 19 dry gels mentioned above are put into the vitrification oven and brought to the

  room temperature at 2000C at the heating rate

  60 C / hour. After maintaining the material at C for 3 hours, it is heated to 300 ° C. at a rate of 60 ° C./hour and maintained at 300 ° C. for 5 hours in order to eliminate the absorbed water. The dry gels obtained at 950 ° C were then heated at 180 ° C./hour and maintained at 950 ° C. for 18 hours to remove carbon and ammonium chloride. We still heat the gels

  dried at 1220 C at a speed of 180 C and are then

  at 1220 C for 1.5 hours to become

  not porous. This gives the transparent tubular silica glass (2.5 cm outside diameter,

  1.5 cm inside diameter and 50 cm in length).

  In the vitrification process, no dry gel breaks and 19 tubular glasses are obtained.

  silica intact, the yield is thus 100%.

  In addition, there is no devitrification or foaming of the obtained silica tubular glass and its

quality is excellent.

Example 10

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  in commerce, and the solution is violently

  to perform the hydrolysis. We add to the solution

  obtained and with stirring, 900 g of silica in

  ultrafine particles ("Aerosil OX50") whose surface

  this specific is 50 m2 / g) and we apply the vibra-

  ultrasound The mass-forming substances are removed by centrifugal separation to obtain the

  soil in which the silica is dispersed uniformly.

  Normal 0.1 ammonia is added dropwise

on the ground to adjust the pH to 4.0.

  1256 ml of the soil solution obtained is

  naked in the rotating cylindrical container (of a dia-

  inner meter 5 cm and length 100 cm) in vinyl chloride and both ends of which are closed by rubber stoppers. We fix

  the container on the rotating machine, as

  is shown in Figure 1 and rotated at 500 rpm. After rotating for 60 minutes and confirming that the sample is completely freeze-dried, the container is removed from the rotating machine and left overnight. The gel obtained in the box (50 cm in width, 120 cm in length and 20 cm in height) is made of polypropylene having a lid whose openings represent 2.0% of the surface and is 25 C at 60 C at the heating rate of 2 C / hour. By drying the gel at 60 ° C. for 7 hours, a dry gel (with an outer diameter of 4.0 cm, an inside diameter of 2.4 cm and a length of 80 cm) is obtained which is Stable enough to not crack, even at room temperature. 5 of the 20 dry gels formed under the same conditions crack and dry gels are obtained, the yield thus being%. The above-mentioned dry gels are placed in the vitrification oven and are

  room temperature at 300 C at the heating rate

  10 C / hour, the temperature at which the dry gels are kept for 5 hours to eliminate the absorbed water. The dry gels are further heated to 600 ° C. at a heating rate of 320 ° C./hour and maintained at 6000 ° C. for 9 hours to remove carbon and ammonium chloride. The dry gels are further heated to 1400 ° C. at the heating rate of 320 ° C./hour and maintained at 1400 ° C. for half an hour to render them non-porous and the transparent tubular glass is obtained. silica

  (3.2 cm outside diameter, 1.9 cm in diameter

  inside and 64 cm long). In the vitrification process, no dry gel breaks and 15 intact tubular glasses of silica are obtained.

yield is thus 100%.

  Furthermore, in spite of the fact that the silica glass in this example is treated at a relatively high temperature such as 1400 C, there is no foaming in the resulting glasses. This implies that by giving the concentration of the silica in fine particles values of 5 moles per 1 mole of metal alkoxide, the problem of foaming is completely eliminated. Nevertheless, if the concentration

  silica is higher than indicated above, the vitrification temperature must be too high, which

  increases the cost of manufacturing and the

  obtained silica becomes unattractive in practice.

Example 11

  540 ml of 0.02 hydrochloric acid are added

  normal to 624 g of the refined silicon ethoxide

  It is commercially available and the solution is violently shaken to effect hydrolysis. 300 ml of water are added to the solution obtained, then 36 g of the ultrafine silica ("Aerosil OX50" with a specific surface area of 50 m 2 / g) are added with stirring and subjected to ultrasonic vibration for get the soil in which the silica is dispersed

  uniformly. Ammonia is added dropwise

  than 0.1 normal to the soil obtained to adjust the pH to 3.0.

  1256 ml of the soil solution obtained is

  naked in the rotating cylindrical container (inside diameter 5 cm and length 100 cm) made of vinyl chloride and both ends of which are closed by rubber stoppers. The container is fixed on the rotating machine as shown in FIG.

  Figure 1 and rotated at 400 rpm.

  After running for 50 minutes and

  after confirmation that the sample is complete-

  taken in gel, remove the container from the

  China turns and is abandoned for one night.

  We put the gel obtained in the box (50 cm wide, 120 cm long and 20 cm high)

  made of polypropylene having a lid whose opening

  are 0.8% of the surface and are worn

  from 5 ° C. to 60 ° C. at a heating rate of 2 ° C./hour.

  Drying the gel at 60 ° C. for 10 days gives a dry gel (2.5 cm outside diameter, 1.5 cm

  inside diameter and 50 cm in length) which is suf-

  stable so that cracking does not occur even at room temperature. 10 of

  20 dry gels formed under the same conditions were

  dyes and 10 intact dry gels are obtained, the

thus being 50%.

  The above-mentioned dry gels are placed in the vitrification oven and heated from room temperature to 200 ° C. at a heating rate of 10 ° C./hour. After keeping the gels dry at 200 ° C. for 3 hours, the dry gels are brought to 300 ° C. at a heating rate of 10 ° C./hour and maintained at 300 ° C. for 5 hours in order to eliminate the absorbed water. The dry gels are further heated to 600 ° C. at a heating rate of 30 ° C./hour and maintained at 600 ° C. for 18 hours to remove carbon and ammonium chloride. The temperature is then raised to 1000 ° C. at a rate of 30 ° C./ hour and the dry gels are maintained at 1000 ° C. for 1.5 hours to render them non-porous and the transparent tubular glass of silica (from 2 cm in outer diameter, 1.2 cm in inner diameter and 40 cm in length). In the vitrification process, 3 dry gels crack and 7 intact silica tubular glasses are obtained.

yield is thus 70%.

  The experiment carried out afterwards demonstrated that, when the silica glasses obtained are maintained at 1200 ° C. for 30 minutes, no foaming takes place.

  but when kept at 1300 C,

  foaming. Similarly, when the concentration of the silica in ultrafine particles is less than 0.2 mol, foaming takes place at 1200 ° C.

  all samples. As a result, the concentration

  silica in ultrafine particles should be

  0.2 mol or more.

Example 12

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of refined silicon ethoxide available

  in commerce, and the solution is violently

  to perform the hydrolysis. 126 g of silica in ultrafine particles ("Aerosil OX50") whose surface is then added to the solution obtained with stirring.

  specific is 50 m2 / g) and is subjected to vibra-

  ultrasound The mass-forming substances are then removed by centrifugal separation to obtain

  the soil in which the silica is dispersed from a

  uniform. Ammonium is added dropwise

  normal 0.1 nia on the ground to adjust the pH to 6.0.

  1256 ml of the soil solution obtained is

  naked in the rotating cylindrical container (inside diameter 5 cm and length 100 cm) made of vinyl chloride and both ends of which are closed by rubber stoppers. The container is fixed on the rotating machine as shown in FIG.

  Figure 1 and rotated at 1500 rpm.

  After rotating for 15 minutes and confirming that the sample is completely set in gel, remove the container from the rotating machine

and we leave it overnight.

  The gel obtained is placed in the box (50 cm wide, 120 cm long and 20 cm high)

  made of polypropylene having a lid whose opening

  tures represent 2.0% of the surface and are worn

  from 5 ° C. to 60 ° C. at a heating rate of 5 ° C./hour.

  Drying the gel at 65 ° C. for 16 days gives a dry gel (2.8 cm outer diameter, 1.7 cm inner diameter and 56 cm long) which is stable enough that it does not occur. cracking even at room temperature. The 20

  Dry gels formed under the same conditions are

  tacts and there is no cracking, the yield

thus being 100%.

  The resulting dry gels are placed in the vitrification oven and are brought from room temperature to 200 ° C. at a heating rate of 60 ° C./hour. After keeping the gels dry at 200 ° C. for 3 hours, the dry gels are again heated at 300 ° C. at a heating rate of 400 ° C./hour and maintained at 300 ° C. for 5 hours to eliminate it. water absorbed. Dry gels are brought at 1000 ° C. at a rate of 400 ° C./hour and maintained at 1000 ° C. for 8 days to remove carbon and ammonium chloride. The temperature is further raised to 1150 ° C. at a rate of 400 ° C./ hour, at which temperature the dry gels are kept for 1.5 hours to render them non-porous and a glass is obtained.

  transparent tubular silica (2.2 cm diameter

  outside, 1.4 cm inside diameter and

  45 cm long). In the vitrifying process

  cation, 2 dry gels crack and 18 intact tubular silica glasses are obtained, the yield

  thus being 90%. Moreover, there is no

  Trification or foaming in silica glasses

and their quality is excellent.

  It emerges from this example that by adopting a high pH for the soil, the production yield of dry gel is almost 100%, which shows good reproducibility. However, if the soil pH is above 6.0, the time required for freezing becomes extremely short and it is difficult to master the material, which

  is a disadvantage for practical use.

Example 13

  840 ml of 0.01 hydrochloric acid are added

  normal to 624 g of the refined silicon ethoxide

  It is commercially available and the solution is violently shaken to effect hydrolysis. 219 g of silica in ultrafine particles ("Aerosil OX50" with a specific surface area of 50 m 2 / g) are added to the solution obtained and with stirring.

  ultrasonic vibration. The strong substances are eliminated

  mass mant by centrifugal separation to get

  the soil in which the silica is dispersed uniformly

  is lying. Normal 0.1 ammonia is added to the soil

to adjust the pH to 4.1.

  1256 ml of the resulting soil solution are poured in

  in the rotating cylindrical container (inner diameter

  5 cm thick and 100 cm long) made of vinyl chloride and both ends of which are closed by rubber stoppers. The container is fixed on the rotating machine as shown in Figure 1 and rotated at 1000 rpm. After rotating for 50 minutes and confirming that the sample is completely freeze-dried, remove the container from the rotating machine and

leave it overnight.

  The gel obtained in the box (50 cm in width, 120 cm in length and 20 cm in height) is made of polypropylene having a lid whose openings represent 0.5% of the surface and is

   C at 120 C at the heating rate of 2 C / hour.

  Drying the gel at 120 ° C. for 4 days gives a dry gel (3.5 cm outside diameter, 2.1 cm

  inner diameter and 70 cm in length) which is suf-

  stable so that it does not occur

  even at room temperature. 6 of 20

  Dry gels formed under the same conditions become

  slow, and 14 intact dry gels are obtained, the

being thus 70%.

  The 14 dry gels mentioned above are put into the vitrification oven and brought to the

  room temperature at 400 C at the heating rate

  60 C / hour to eliminate the absorbed water. The dry gels are still carried at 1100 ° C. at a heating rate of 180 ° C./ hour and maintained at 1100 ° C.

  for 3 hours to remove carbon and chlorine

  ammonium chloride. Then we raise the temperature to

  1220 C at a speed of 180 C / hour, temperature at

  the dry gels are held for 1.5 hours to make them non-porous and the transparent silica tubular glass (2.5 cm outer diameter, 1.5 cm inner diameter and 50 in length) is obtained. In the vitrification process, 3 gels

  dry and split into 11 tubular glasses.

  silica rests intact, the yield thus being

78.6%.

Example 14

  840 ml of 0.05 hydrochloric acid

  normal to 624 g of refined silicon ethoxide available

  in commerce, and the solution is violently

  to perform the hydrolysis. 219 g of the ultrafine silica ("Aerosil OX50" with a specific surface area of 50 m 2 / g) are then added to the solution obtained and with stirring, and subjected to ultrasonic vibration. The mass-forming substances are removed by centrifugal separation to obtain the sol in which the silica is dispersed uniformly. 0.1 ammonia is added to the soil

normal to adjust the pH to 5.0.

  1256 ml of the soil solution obtained is

  naked in the rotating cylindrical container (inside diameter 5 cm and length 100 cm) made of vinyl chloride and both ends of which are closed by rubber stoppers. The container is fixed on the rotating machine as shown in Figure 1 and rotated at 2000 rpm. After

  have been running for 30 minutes, with confirmation

  If the sample is completely set in gel, remove the container from the rotating machine and

leave it overnight.

  The gel obtained in the bundle (50 cm in width, 120 cm in length and 20 cm in height) is made of polypropylene having a lid whose openings represent 5.0% of the surface and is brought from C to 20 C. the heating rate of 120 C / hour. Drying the gel at 20 ° C. for 22 days gives a dry gel (3.7 cm outer diameter, 2.2 cm inner diameter and 74 cm long) which is sufficiently stable so that it does not occur. cracking even at room temperature. 16 of

  Dry gels formed under the same conditions were

  dyes and we obtain 4 dry gels intact, making it

thus being 20%.

  The 4 dry gels mentioned above are put in the vitrification oven and they are

  room temperature at 200 C at a heating rate

  fage of 10 C / hour. After maintaining the dry gels at 200 ° C. for 2 hours, they are further heated to 300 ° C. at a heating rate of 10 ° C./hour and

  they are kept at 300 ° C for 2 hours to eliminate

  absorbed water. The dry gels are brought to 950 ° C. at a rate of 180 ° C./hour and maintained at 900 ° C. for 6 hours to remove carbon and ammonium chloride. The temperature is further raised to 1220 ° C. at a rate of 180 ° C./ hour, at which temperature the dry gels are held for 1.5 hours to render them non-porous and the transparent tubular silica glass (2.5 ° C.) is obtained. cm outer diameter, 1.5 cm inner diameter and 50 cm length). During the vitrification process, no

  dry gel does not crack and we obtain 4 tubular glasses

  silica films intact, the yield is thus 100%. In addition, there is no devitrification or foaming in the tubular silica glass obtained

and its quality is excellent.

  As described above, with reference to Examples and according to the invention, a large tubular silica glass is obtained which was impossible to obtain by the conventional sol-gel process. In addition, the quality of the following tubular silica glass

  the invention is excellent from the point of view of the

  optical characteristics. Moreover, it is possible to ob-

  keep a very high manufacturing yield such as% and more. The present invention thus provides a tubular silica glass as a material for a

  optical fiber at a very low cost.

  In another example of a conventional method of

  preparation of tubular silica glasses,

  the soil solution in which the silica in

  ultrafine particles is added to the hydro-

  lysed alkyl silicate by an acid catalyst,

  in the cylindrical container, while making

  The container is then dried and vitrified to obtain the tubular silica glass with an outer diameter of 2.6 cm, an internal diameter of 1.6 cm and a length of 52 cm at most. As the dry gel obtained in the above process has large pores and as the combining force between the ultrafine silica particle that is included is more

  only in the silica gel prepared by the procedure

  previous dice following Ravinovich, we can easily

  a large tubular silica glass. In addition, as the gel setting is performed by rotating the container, the resulting gel is larger and it is

  rounded in a more uniform way.

  The techniques mentioned above include

  all of them a uniform stage of dispersion of

  silica particles in the liquid phase. In order to disperse the powder-like material in the liquid, stirring, the application of ultrasonic vibration, etc. are generally used. In any case, it takes a lot of energy and time to uniformly disperse the powder in the solution, and it is difficult to obtain the solution in which the dispersion is perfectly uniform. But if a mass-forming substance remains in the finished glass, such a mass is a defect of the product, which decreases the quality of the glass. In addition, silica usually on the market generally includes impurities

  such as A1 and Fe in a quantity of a few

  per million to a few hundred parts per million and does not represent a favorable

  for the optical glass according to the invention.

  The invention overcomes these disadvantages by a

  an improved method of preparing a tubular glass

  high quality silica by controlling the high purity of the soil in which the particles of

  silica are dispersed uniformly.

  The process according to the invention consists of

  to make the soil of a solution into a tubular form

  To which is a solution of hydrogen alkyl silicate

  lysed by an acid catalyst and a solution B which is a solution of hydrolyzed alkyl silicate

  by a basic catalyst, to dry this gel to obtain

  a dry gel and vitrify this dry gel to form

a transparent glass.

  The size of the SiO particle from the hydrolysis of the alkyl silicate varies depending on the catalyst used. In particular, when using a basic catalyst, it is possible to obtain a silica particle of larger size than in

  - the case where an acid catalyst is used and the

  the silica particle can be defined at will by adjusting conditions such as

  amount of catalyst, the amount of silicate -

  of alkyl relative to the solvent, the amount of water, the temperature, etc. To obtain the large dry gel

  and, as a result, the glass of silica, it is essen-

  that dry gel has large pores. The particle

  relatively large solution B satisfies

  made to the above requirement and the small particle included in solution A has the effect of enhancing the combining force between the silica particles of solution B. In view of the above, if the particle diameter of the silica included in solution B is 0.01 meter or less than this value, the expected effect is not obtained and if this particle diameter is too large, the silica particles are deposited, which is a drawback for obtain the soil solution in which the silica is dispersed in a uniform manner. In particular, according to the invention, where the sol is taken in gel by rotation, the acceptable diameter of silica particles is

  a maximum of 1,000 m if we consider the influence

  this of the centrifugal force. As mentioned above, according to the invention, the sol is obtained by mixing a solution A and a solution B, both in

  liquid phase and thus there is no particular stage

  bind to disperse the silica particles. In-

  the agent used can be refined easily,

  so that the material has excellent purity.

  The concentration of silica in the solution

  B is generally very small, although it varies

  the conditions of synthesis. This is because, unless the amount of the solvent is large relative to the alkyl silicate to some extent at the time of synthesis, it is impossible

  to obtain silica particles of uniform diameter

  form. To form the dry gel with a good yield, it is better that the concentration of the silica in

  the soil is high, but if it is too high, the

  particle persion in the soil becomes non-uniform

  me and entails a decrease in the quality of the product. -

  It follows from the need to focus the

  solution B. In view of the above, the concentration of

  The desired solution silica solution is

3 3

  between 0.15 g / cm and 1.0 g / cm3.

  The characteristic of the dry gel formed is

  relationship with the rate of mixing of the solu-

  A and B. As mentioned above,

  the higher the rate of mixing of solution A, the more the pores included in the dry gel are

  small, which makes breaks and cracks

  are more likely to occur. On the other hand, if the mixing ratio of the Best solution increased, the pore itself becomes actually large, but with the disadvantages that the dry gel strength drops

  and that a high temperature is required for the vitrification

  cation. In view of the foregoing, in order to obtain large size silica glass of good quality, the mixing ratio of solution A and solution B is such that the molar amount of silica of the AM solution (A) ) relative to that of the solution BM (B) must be between 0.2 and 3,

  that is, M (A) / M (B) = 0.2 to 3.

  The time required for gel setting of the silica sol as above, according to the invention, depends greatly on the pH of the soil. In general, when the soil pH is about 6, the time required for

  gel is so short that gel

  kill instantly. If the soil pH is less than 3, the stable state of the soil lasts for quite a long time. By directly mixing solution A and solution B, the acid and the base are neutralized and the pH of the mixed soil is about 6. It follows that the

  soil is quickly taken in gel, which is a

  venient. Therefore, to define the soil pH

  the desired value, it is necessary to adjust the

  the pH of solution A and solution B before mixing. The possible methods for adjusting the pH of mixed soil are: (1) lowering the pH of solution A, (2) lowering the pH of solution B, and (3) lowering the pH of both solution A and Solution B. Regardless of the method used among the three listed above, the condition of the soil next and the quality of the final product are the same. Instead, it is also possible to adjust the pH of the soil solution after mixing by addition of ammonia, hydrochloric acid or other

* similar product.

  Referring now to FIG.

  the rotating machine to form the cylindrical gel

drique.

  The soil solution, whose pH is adjusted to

  described above, is poured into the cylindrical container and the container is attached to the rotating machine and the soil is gelled by rotating the container. Such a gel in rotation, as above, gives a cylindrical gel whose roundness

is very good.

  The conditions of rotation for the taking into

  Rotational freeze are described below. As men-

  mentioned above, the material used according to the invention

  silica particles of which the diameter is

  The particle size is between 0.01 micron and 1.0 micron. Silica is deposited under the effect of the centrifugal force caused by the rotation, which renders the composition of the soil, and therefore the

  gel. The lack of uniformity of the gel causes not only

  the cracking of the gel at the time of drying or vitrification, but also decreases the optical properties of the gel obtained. That's why you have to adjust the number of revolutions and the rotation time

  that the silica particles in the soil are not deposited

not feel.

  The parameters for adjusting the deposit of

  silica particles are, for a given size of the tubular silica glass, the number of turns and the

  duration of rotation when gel is rotated

  soil composition and composition. Among these parameters, the duration of rotation is necessarily determined by the duration required for the setting in gel and by the yield of the dry gel and the composition of the soil is

2-571357

  optimized for vitrification. It's for-

  what the deposition of the silica particles must be

  mainly by the number of turns. This number of turns is adjusted in accordance with what has been indicated previously. When a dry gel of large size is prepared, the yield is lowered if the container

  and the drying conditions are not adequate.

  The following is an explanation of the recital

  appropriate drying conditions and drying conditions

to improve performance.

  The stage of drying a wet gel in a dry gel has a great influence on the yield. For

  make the contraction of the wet gel without cracking

  the interior of the wet gel is uniformly dried.

  The wet gel therefore needs to be dried slowly. But from the point of view of productivity, it is proposed to put the gel in the container coated with lid whose openings represent at least 10% of the surface, to wear the gel between 40 and 160 C at a heating rate of less than 120 C / hour and dry the gel at this temperature. By these methods, the dry gel is obtained in a relatively short time with a good yield. At this time, if a wet gel is dried in the rotating cylindrical container in which the wet and formed gel is covered and the covers whose openings are 10% of the surface, the dry gel is easily obtained in good yield. However, if we place a wet gel

  in another container whose lid has openings

  10% of the surface, and if the wet gel is then dried, the yield is further improved.

  dry gel formation. The most desirable process

  to improve productivity without lowering the

  yield, is to replace all the moisture gels

  in another container as above and dry them.

  In the process for the preparation of tubular glass

  according to the invention, the vitrification stage

  Dry gel cation encompasses the following seven stages.

  Among these stages, stages (4) and (5) can be omitted. When the tubular silica glass for a

  optical fiber should be used as a

  the OH group content of the silica glass must be less than one part per million. In one case

  such as this, stage (4) of elimination of the group

  OH with the chloride and the subsequent stage (5) of chloride removal are necessary. But when

  the tubular silica glass is used as tube-

  envelope to adjust the outer diameter of the optical fiber, even if the content of the OH group is a few hundred parts per million, there is little problem. This is why the required quality

  for silica tubular glass depends on its use

  and stages (4) and (5) are not always necessary. (1) Elimination of absorbed water, (2) removal of carbon,

  (3) acceleration of the condensation reaction

  with dehydration, (4) removal of the OH group, (5) removal of chloride or fluoride, (6) pore closure in the dry gel,

  (7) transformation of the dry gel into transparent glass.

  The stage (1) of removal of absorbed water has a great effect on the yield of dry gel in the vitrification process. Water absorbed physically in the dry gel in a large quantity may

  be removed by heat treatment at approximately 400 ° C.

  If the dry gel is suddenly heated to such a

  high temperature, it is likely that

  occur, which decreases the yield. But if the heating rate is too low, it takes a long time for the treatment and the manufacturing cost increases. Extensive studies and experiments have found that it is best to remove the absorbed water in at least one stage of heating.

  dry gel at the temperature determined in advance,

  less than 400 C at a heating rate of not more than

  400 C / hour and keeping the gel dry at room temperature

  at least one hour. By keeping the gel dry at the temperature determined in advance for at least one hour, the water is uniformly eliminated.

  absorbed in the dry gel, which improves the efficiency

  is lying. In stage (2), the carbon in the dry gel is removed by the heat treatment at a temperature between 400 and 900 C. At the same time, the ammonia base is also removed and the acid (ammonium salt) is removed. found inside the gel. As for stage (1), the heating rate has an effect on the efficiency and the appropriate heating rate is between 30 and 400 C / hour in practice. In addition, the stage (2) can be carried out in atmospheres comprising

gaseous oxygen.

  In step (3), the reaction of

  concentration by dehydration by at least one stage of heating the dry gel at the temperature of 900 to 1200 ° C. and at the heating rate of 30 to 400 ° C./hour and keeping the gel dry at the chosen temperature for 30 minutes at less. The purpose of this

  stage (3) is to accelerate the concentration reaction.

  by dehydration inside the gel for

  reduce the number of unreacted OH groups.

  If step 3 is omitted and the next stage is carried out, when the OH group is removed, the OH group removal agent is consumed in a large amount and foaming often occurs.

  the dry gel is transformed into a transparent glass.

  As in the previous stages, the heating rate at stage (3) also has an effect on the

  yield, but the range mentioned above is suitable.

  The goal of stage (4) is to eliminate the group

  OH in the dry gel, which is a particular parameter

  important to undermine the characteris-

  transmission of the optical fiber obtained

  naked. In stage (4), the OH group is removed by heating.

  dry gel at a temperature between 700 and 1100 C with flow of a carrier gas not including impurities such as water, etc., and the agent

  the elimination of the OH group in an amount which is

  the representative of 1 to 40% of the carrier gas

  in the vitrification oven. To eliminate completely

  Preferably, the OH group, the concentration of the OH removal agent relative to the carrier gas must be greater than 1% and is advantageously between 1 and 40%. As an agent eliminating the

  OH group used in stage (4), the reaction

  tif which is transformed into (Si-Cl) or (Si-F) by reaction on (Si-OH). In consideration of the cost and ease of handling, in principle

C12, SOC12, SF6, CF4, C2F6 and C3F8.

  The goal of stage (5) is to eliminate the

  the fluoride existing in the gel after the

  the OH group at the previous stage. If step (5) is omitted and vitrification is carried out, the chloride or fluoride in the silica glass causes foaming when the dry gel is converted into a clear glass, or when the optical fiber is made from the glass by fiber drawing. The chloride or fluoride is removed by flowing the carrier gas such as He and O 2 in an amount of between 1 and% relative to the carrier gas in the vitrification furnace, at a temperature of between 800.degree.

and 12000C.

  In step (6), the pores of the dry gel are closed by heating, while placing the inside of the oven under vacuum or by flowing helium gas into the oven. If the pores of the dry gel are closed without performing the above operation, the gas of

  the atmosphere is enclosed in the pores, which

  the foaming of the dry gel when it is transformed into a transparent glass. The heating rate has an effect on the efficiency. The appropriate heating rate is between 30 and 400 ° C./hour. The temperature at which the closed pores are produced in the glass varies depending on the mixing rate of

  solution A and solution B in the soil of

  of the concentration of silica in the soil, the mean diameter of the particles of the silica included in solution B, the distribution of the diameter of the particles of the silica included in solution B, the distribution of the pore diameter in the freeze,

  the water content of the gel, the rate of heating

  age, etc. This is why it is necessary to carry out a research on the reagent used for the pore closing stage. According to the operating mode of the invention, the temperature at which the

  pores is between 900 and 1350 C.

  In stage (7), after pore closure, the gel is heated to a temperature of between 1200 and 1600 ° C. and is maintained at this temperature

2 5 7 1 3 5-7

  for a period determined in advance for trans-

  form the dry gel into a clear glass and, finally,

  The result is tubular silica glass.

  In the process for the preparation of tubular glass

  silica gel according to the invention, the program

  optimum temperature for each of the stages

  above in the sintering process is different

  according to the mixing ratio of solution A and solution B to prepare the soil, according to the concentration of silica in the soil, according to the mean diameter of the silica particles included in solution B, according to the distribution of the diameter of the silica particles included in solution B, depending on the distribution of the pore diameter in the gel, depending on the water content of the gel, etc. This is why we choose the optimal temperature and optimal heating rate at each stage in the

  corresponding range as mentioned above.

  The process described above provides a glass

  tubular silica of high quality which is sufficient

  large, and that in a good performance. The examples

  following plots illustrate the invention.

Example 1

  (1) Preparation of the solution A. 200 g of 0.02 hydrochloric acid are added

  579.0 g of the refined ethyl silicate available

  in commerce, and the solution is violently

  to perform the hydrolysis. The solution is

obtained "solution A".

  (2) Preparation of Solution B. 2187 g of anhydrous ethanol, 72 ml of ammonia and 300 g of water were added to 864.9 g of commercially available refined ethyl silicate. The solution is stirred for 2 hours and left overnight. The solution obtained is designated as "solution B". The diameter of the particles measured by a device for measuring the ganulometry is in

average of 0.15 micron.

  (3) Concentration of solution B. Concentrate solution B prepared at the stage

  2 under reduced pressure so that the concentration

  silica treatment of 0.06 g / cm3 of the solution of

starting at 0.40 g / cm3.

  (4) pH adjustment before mixing.

  The pH of the concentrated solution B and the

  Solution A are 8.30 and 2.10, respectively.

  By the addition of 2 times normal hydrochloric acid, the pH of the solution is adjusted to 5.0. We again measure the particle diameter of the silica of the

  solution B obtained by the grading device

  nullometry and it turns out that the diameter of the particles

is the same as in stage (2).

(5) Mixing.

  650 ml of solution A prepared in stages (1) and 620 ml of solution B prepared in

  stage (4) in a mixing ratio such that the concentration

  silica in solution A M (A) relative to that in solution B M (B), that is M (A) /

  M (B) is 0.67. The pH of the mixture is 4.80.

(6) Rotational gelation.

  Referring to Figure 1 which shows schematically the rotating machine used for

gel taking by rotation.

  1256 ml of the prepared soil solution is poured into

  at stage (5) in a steel jacket tube

  vinyl chloride, the dimensions of which are

  inside of 5 cm and a length of 100 cm. The two ends of the steel tube are covered with silicone rubber and the container is fixed in the rotary machine shown in FIG. 1. The container is then rotated at a speed of 700.degree.

  revolutions per minute until a sample is

  completely taken in gel. It takes 65 minutes for

  the sample is completely set in gel. We ob-

  then holds a moist gel of 5 cm in outer diameter, 3 cm in inner diameter and 98 cm in length.

(7) Drying.

  10 wet gels obtained in stage (6) are kept in the rotating steel tube for 2 days and placed in the steel box (15 cm long, 120 cm wide and 20 cm high) having an opening lid representing 1% of the surface. The wet gel is then brought from room temperature (25 ° C.) to 70 ° C. at a heating rate of 2 ° C./hour. After keeping the gel wet at 70 ° C for 12 days, a dry gel (3.3 cm outer diameter, 2.0 cm inner diameter and 64 cm length) is obtained which is sufficiently stable for it to become does not produce cracking even at the

ambient temperature.

(8) Vitrification.

  The dry gel obtained is placed in the tube furnace.

  vitrification glass made of quartz glass and heated from 30 C at the heating rate of C / hour. After keeping the gel dry at 200 ° C. for 5 hours, the dry gel is heated to 300 ° C. at a heating rate of 30 ° C./hour and is maintained

  at 3000C for 5 hours to remove the absorbed water.

  The dry gel is then further heated from 300 ° C. to 1100 ° C. at a rate of 30 ° C./hour and is maintained at 1100 ° C. for 30 minutes in order to remove carbon and ammonium chloride and to accelerate the reaction.

condensation with dehydration.

  The temperature is brought to 7000 ° C. and the gel is kept dry at 700 ° C. for 30 minutes, while flowing a gaseous mixture of He and

  Cl2 at Kdebits of 2 liters / minute and 0.2 liters / minute.

  The dry gel is then heated to 800 ° C. at a heating rate of 60 ° C./ hour, while He only flows and is maintained at 800 ° C. for one hour, while flowing the gas mixture He and Cl2 auK flow rates of 2 liters / minute and 0.2 liter / minute. The dry gel is further heated to 9000 C at the heating rate of 60 C / hour, while flowing only He, and maintained at 900C for one hour while flowing

  the gaseous mixture of He and Cl2 at the level of 2 liters

  very minute and 0.2 liter / minute, / to remove the OH group. Then the dry gel is brought to 1050 C at the heating rate of 60 C / hour, while flowing the gaseous mixture of He and O2 Kdebits

  of 2 liters / minute and 0.4 liters / minute and

  holds at 1050 C for one hour to remove the chloride. The dry gel is heated to 1250 ° C. at a heating rate of 30 ° C./hour, while He only flows and is maintained at 1250 ° C. for one hour in order to close the pores of the gel. Then place the sample in the oven and bring it to 1200C

  at 1350 C at the heating rate of 60 C / hour.

  Maintained at 13500C for one hour, the dry gel

  comes non-porous and one obtains the transparent tubular glass of silica (external diameter of 2.6 cm,

  inner diameter of 1.5 cm and length of 50 cm).

  During the vitrification process, there is no cracking and the yield is%. The amount of OH group included in the silica tubular glass obtained by the infrared absorption spectrum is measured and there is no

  peak of absorption when the wavelength of

  infrared radiation is 2.70 microns, indicating that the amount of OH groups is of the order of

  part per million or less than this value.

  Precision dimensions of silica glass

  obtained with regard to the tolerance on the dia-

  indoor and outdoor mothers is + 1% or is

less than this value.

  We do not observe either inclusion or

of impurities.

  In addition, even if heated,

  annular heating system, the tubular silica glass obtained until it is molten, it does not

no foaming occurs.

  Thus, it turns out that the tubular silica glass obtained can be applied to manufacture a

optical fiber.

  Another dry gel is vitrified, formed in the same manner as above before vitrification, in the following manner. The dry gel is placed in the tubular quartz vitrification furnace and is

  2000C at the heating rate of 30 C / hour,

  it is maintained for 5 hours.

  Then the dry gel of 2000 C is brought to 300 C at the speed of

  heating of 30 C / hour and is maintained at

  3000C for 5 hours to remove the absorbed water.

  The dry gel is further heated from 3000 ° C. to 1000 ° C. at room temperature.

  heating rate of 30 C / hour and maintained at 10000 C for 10 hours to remove carbon and ammonium chloride and to accelerate the reaction

  condensation with dehydration.

  The dry gel obtained is heated further to 11000 C.

  at the heating rate of 60 C / hour, it is maintained there

  hold for 20 hours, it is brought to 1150 C at the speed of 60 C / hour and kept there for hours to accelerate the condensation reaction

  with dehydration in the state where the pores are

  greens and to decrease the amount of OH group. Then

  the dry gel is brought to 1250 C at the heating rate.

  30 C / hour while flowing He at the rate of 2 liters / minute and maintained at 1250 C for one hour to close the pores. We replace the material in the oven and bring it from 12500 C to

  1350 C at the heating rate of 60 C / hour.

  After maintaining the dry gel at 1350 ° C. for one hour, the dry gel becomes non-porous and

  transparent tubular glass of silica.

  The amount of OH group in the silica glass obtained is 400 parts per million. Even if the silica glass is heated to 20000 C to bring it to the molten state by means of a

  annular heating, there is no foaming.

  Thus, despite the fact that the stage of elimination

  of the OH group using chloride and others and the accompanying stage of removal of the chloride have been omitted, a satisfactory silica tubular glass is obtained which can be used as a sheath tube for adjusting the outer diameter

an optical fiber.

Example 2

  In Example 2, step 2 of Preparation B of Example 1 is replaced by the following: 2500 ml of anhydrous ethanol, 250 ml are added

  of ammonia (29%) and 165 g of water with 468 g of

  refined ethyl ester and the solution is stirred

  2 hours and let it rest for one night.

  The particle size of the silica included in the solution is measured by a particle size measuring device and the average particle diameter is found to be 0.34 microns. The diameter of

  silica particles that settle to the bottom of the container.

  after being once abandoned, is 1 micron or more. The foregoing shows that silica particles having a particle diameter greater than 1 micron included in the soil have a disadvantage in obtaining soil in which the silica particles are dispersed uniformly. Following the chlorine removal step as indicated in Example 1 ', the water content is reduced to less than one part per million and

  a tubular glass of silica of high quality.

Example 3

  In preparing solution A, the hy-

  drolysis using normal nitric acid,

the same way as in Example 1 '.

  Solution B is prepared and concentrated in the same manner as in Example 1 '. Then the pH of the concentrated solution B is adjusted to 4.0 by addition

  ammonia 2 times normal and mixed with

  A. The pH of the mixed soil is 3.2. Such a soil with a low pH such as 3.2 does not gel, even

  if it is kept for a few days at

  ambient temperature. This is why we adjust the pH of

  soil at 4.90 by the dropwise addition of ammonia

than normal 0.2.

  The soil is gelled by rotation to obtain a wet gel in the same manner as in Example 1 ', except that the rotational speed is 100 rpm. The wet gel obtained is converted into the gel

  dry in the same way as in Example 1 '.

  The dry gel obtained is placed in the vitreous oven.

  Tubular quartz glass fication and is heated from 30 ° C. to 2000 ° C. at a heating rate of 30 ° C./hour and maintained at 200 ° C. for 5 hours. The dry gel is further heated from 200 ° C. to 300 ° C. at a heating rate of 30 ° C./hour and is maintained at 300 ° C. for 5 hours in order to eliminate the absorbed water. The dry gel is then heated from 300 ° C. to 1000 ° C. at a heating rate of 30 ° C./hour and maintained at 1000 ° C. for 60 minutes to remove the carbon.

  and ammonium chloride and to accelerate the reaction

  condensation by dehydration. It is cooled to 800 ° C. and the gel is maintained at 800 ° C. for 30 minutes, while flushing the gaseous mixture of He and C12 at a rate of 2 liters / minute and 0.2 liter / minute. The material is heated to 900.degree. C. at a heating rate of 60.degree. C./hour, while He only flows and is maintained at 9000.degree.

  for an hour while flushing the mixture

  He gas and Cl2 gas at 2 liters / minute and 0.2 liter / minute. The dry gel is further heated to 1050 ° C. at a rate of 60 ° C./ hour, while flowing the gaseous mixture of He and O 2 atmobits.

  of 2 liters / minute and 0.4 liters / minute and it is

  holds at 1050 C for one hour to remove the chloride. Then, the dry gel is brought to 1250 ° C. at a heating rate of 30 ° C./ hour, while He only flows and is maintained at 1250 ° C.

  for 30 minutes to close the pores. -

  The material is returned to the oven and is heated from 1200 ° C. to 1350 ° C. at a heating rate of 60 ° C./hour. Maintained at 1350 ° C for one hour, the dry gel becomes non-porous and the glass is obtained

tubular transparent silica.

  The amount of OH group included in the -

  Silica glass obtained is about 10 parts per million in the center of the glass. There is no foaming, even if we pass the silica glass to the state

melted by heating.

Example 4

  Solution A and Solution B are prepared in the same manner as in Example 1, and the conditions are varied experimentally in various ways.

concentration of solution B in stage (3).

  (There are 3 samples used for

  each of the 4 experiments, which makes a total of

  samples of 12). Since the volume ratio of solution A and solution B is different

  in each case, the pH of the mixture is different.

  This is why the final pH of the mixture of the two solutions is adjusted to 5.0 by the addition of 0.1 ammonia.

  normal and 0.1 hydrochloric acid normal.

  The results of the above experiment are

shown in the following table.

  Silica concentration (g / cm3) Condition of dry gel (g / cm3) I> .ç Sol (0,06) 0,10 O

0.15 O

o, 0 0 0

0.20

  In the table above, D, O and Q show that the dry gel obtained is broken, that the dry gel obtained is cracked and that the dry gel obtained is

perfect respectively.

  The results above show that the

  Amendment B should be concentrated until the

  the center of the silica within it becomes superior

  less than 0.15 g / cm3. Then we vitrify even cracked gels or

  broken in the same way as in Example 1, and

  holds a silica glass of excellent quality.

  When we condense solution B, then

  the silica concentration exceeds 1.0 g / cm3, the screw

  cosity of the solution increases sharply, which allows to obtain the solution in which the silica is dispersed uniformly. Therefore, there is no advantage in concentrating solution B until the concentration of silica is greater than

1.0 g / cm.

Example 5

  The experimentation rate is experimentally

  mixture of solution A and solution B. The

  The stages of soil preparation, drying and vitrification are the same as in Example 1 (3 samples are used for each of the 6 types of mixing ratio, ie 18 samples in total). In the same way as in Example 4 ', the pH of the mixture is

  different, since the volume ratio of the solu-

  A and solution B are different for each mixing ratio. This is why we adjust the final pH

  of the mixed solution to 5.0 by adding ammonia

  than normal 0.1 or 0.1 hydrochloric acid

normal.

  The results of the above experiments are

shown in the table below.

  M (A) / M (B) Condition After frost freeze vitrification Quality 0.1 OO 0 0 Good 0.2 OOOOOO Good 0.5 QQQ 0 OO Good 1 00 0 0 0 Good 3 0 Bullage 0 (Foaming Results above indicate that, for

  to obtain large silica tubular glass

  the mixing ratio of solution A. and solution B, in terms of the concentration of silica included

be between 0.2 and 3.

Example 6

  Five tubular wet gels are formed in the same stages as in Example 1 '. The wet gels are dried in the rotating container used for

  gelation without placing them in another container

  tainer. We cover both ends of the container

  lids each having openings

  as much as 1% of the lid area. The wet gels in the container are dried in a thermostatically controlled chamber at 60 C. 3 of the 5 gels break during the drying stage above and the remaining 2 dry gels do not break or crack, but are curved in a manner considerable in comparison to those

obtained in Example 1 '.

Example 7

  Five tubular wet gels are formed in the same stages as in Example 1 '. The wet gels are replaced in drying containers with different opening rates. The gels are dried in a thermostatically controlled chamber at 60 ° C. and the state of the

dried gels.

  The results of the experiments are indicated

in the following table.

  Container opening rate Dry frost condition (%) Split at room temperature Split in 2 days Split in 10 days 0.5 Perfect (dried in 25 days) The table above shows that even though the container opening is between 5 and 10%, it may be possible to prevent the gel from cracking when drying at low temperature. But it takes a long time to completely dry the gel;

  the process is of poor efficiency. By using

  In the drying container having an opening rate of 0.5%, the intact dry gel formation efficiency is good, but it takes a fairly long time, such as 25 days, to complete the drying. Therefore, considering the time required for drying and the yield, the appropriate opening rate for the drying container is between 1 and 2%

Example 8

  The soil is prepared in the same way as in Example 1 '. We experimentally vary the

  rotational speed when the gel is rotated

  soil. In all experiments, the final pH

  the soil is adjusted to 5.10 and the effective duration of rotation

  tion (the length of time during which

  until the soil is completely

gel) is 30 minutes.

  The results of the examples are recorded in

following table.

  Centrifugal Rotational Speed of Rotation Condition of the wet gel (rpm) (g) 0.3 No hole in the center 500 7 Good 1000 28 Good 3000 250 Good 6000 1000 Cleaving (particles are deposited)

  In the table above, g = 980 cm / second2.

  The wet gel obtained by rotating at a speed of 3000 rpm has a satisfactory state but, after drying, a peel is observed inside the gel. The reason for this coat would be that the particles

  of silica are deposited under the effect of the cen-

  trifuge, the particle density being low on the inner surface. This implies that a too violent rotation is a disadvantage to obtain a gel

of high quality.

Example 9

  (1) Preparation of Solution A. 300 g of 0.1 normal chloride is added to 635 g of commercially available refined methyl silicate and the solution is shaken violently.

perform the hydrolysis.

  The solution obtained is designated as solution A. (2) Preparation of solution B. 6200 ml of anhydrous methanol, 575 ml

  of ammonia (29%) and 300 g of water with 635 g of

  refined methyl ester available commercially.

  After stirring for 2 hours, the solution is kept at rest overnight. We designate the

  solution obtained as solution B. The

  of the silica particles included in the

  B is measured by a particle size measuring device and found that the average diameter

particles is 0.19 micron.

  (3) Concentration of solution B and adjustment of

its pH.

  The solution B prepared at the stage is concentrated

  (2) under reduced pressure until the concentration

  The silica content becomes 0.45 g / cm 2.

  Then the pH of the concentrated solution B is adjusted

at 4.50.

(4) Mixing and pH adjustment.

  The pH of the mixed solution consisting of 918 ml of solution A and 570 ml of solution B and prepared in stage 3 is 4.35. The pH was adjusted to 4.80 by addition of normal 0.2 ammonia.

(5) Rotational gelation.

  1256 ml of the solution obtained in stage (4) is poured into the chloride-jacketed steel tube.

  of vinyl whose dimensions are of an inte-

  5 cm and a length of 100 cm.

  The ends of the silicone rubber container are covered and fixed on the rotating machine. The container is then rotated at a speed of 1500 rpm until a sample is set in gel. The required duration

  for taking in soil gel is 70 minutes.

  In this stage (7), a tubular wet gel of 5.0 cm outside diameter, 3.0 cm is obtained

  Inner diameter and 98 cm in length.

(6) Drying.

  The wet gel, formed in stage (5), is allowed to stand in the rotating container for 3 days and placed back in the box (15 cm wide,

  cm in length and 20 cm in height) in stainless steel

  having a lid whose openings represent

  feel 1.5% of the surface. By putting it in the

  drying machine, the wet gel is heated

  room temperature (25 C) at 60 C at the heating rate.

  fog of O5 C / hour and kept at 600C

  15 days. Then the dry gel (3.5 cm outer diameter, 2.1 cm internal diameter and 69 cm length) is obtained.

stable enough for him

  splitting does not occur, even at the temperature

ambient temperature.

(7) Vitrification.

  The dry gel obtained is placed in the quartz glass vitrification furnace and is heated from 30 ° C. to 200 ° C. at a heating rate of 30 ° C./hour, at which temperature it is maintained for hours. Then the dry gel is brought from 2000 C to 3000 C

  at the heating rate of 30 C / hour and it is

  hold at 300 C for 5 hours to remove the absorbed water. The dry gel is further heated from 300.degree. C. to 1050.degree. C. at a heating rate of 30.degree.

  keep it at 1050 C for 30 minutes to eliminate

  carbon and ammonium chloride and to

  lerate the condensation reaction with dehydration.

  The material is cooled to 7000 C and maintained

  30 minutes while flowing the gaseous mixture of He and Cl2 in the debits of 2 liters / minute and 0.2 liter / minute. Then we bring the material to 8000C

  at the heating rate of 60 C / hour while

  Only He flows and is kept at 800 ° C. for one hour, while flowing the gaseous mixture of He and Cl 2, at a rate of 2 liters / m 2 and 0.2 1 liter / minute. The dry gel is then heated to 900 ° C. at a rate of 60 ° C./ hour, while flowing He gas only, and is maintained at 900 ° C. for one hour, while flowing the gas mixture He and Cl2 in the ratio of flow rates of 2 liters / minute to 0.2 liters / minute, to remove the OH group. The dry gel is then brought to 1000 ° C. at a rate of 60 ° C./hour, while flowing the gaseous mixture of He and O.sub.2 in the ratio of flowrates of 2 l / min to 0.4 l / min. and maintained at 1000 ° C. for one hour to remove the chloride. Then the dry gel obtained is heated at 1250 ° C. at a rate of 30 ° C./ hour while flowing helium gas only and maintained at 1250 ° C. for 30 minutes for

close the pores in the gel.

  The dry gel is placed in the box and is heated from 1250.degree. C. to 1500.degree. C. at a heating rate of 60.degree. C./ hour and a transparent silica tubular glass (2.7 cm outside diameter, d an inner diameter of 1.6 cm and a length

52 cm).

  Quality, quantity of OH group, etc. silica glass obtained are equal to those of

silica glass of Example 1 '.

  It can therefore be expected to obtain silica glass of equivalent high quality, irrespective of the alkyl group of the alkyl silicate used.

  starting material, following the stages in accordance with

in accordance with the invention.

Example 10

  Tubular dry gel formed in the same way

  that in Example 9 ', is vitrified in the manner

  below: The dry gel is placed in the quartz glass vitrification furnace and is

   C at 2000 C at the heating rate of 30 C / hour.

  After maintaining it at 2000 ° C. for 5 hours, the 2000C dry gel is heated to 3000 ° C. at a heating rate of 30 ° C./hour and maintained at 3000 ° C. for 5 hours in order to eliminate the absorbed water. The dry gel is then heated from 3000 ° C. to 1050 ° C. at a rate of 30 ° C./hour and is maintained at 1050 ° C. for 30 minutes to remove carbon and chloride.

  and to accelerate the condensation reaction.

  with dehydration. The dry gel is cooled to 700 ° C. and maintained at 7000 ° C. for 30 minutes, while flushing the gaseous mixture of He and CF4 in the ratio of flow rates from 2 liters / minute to 0.2 liters / minute. Then the dry gel is heated to 800 C at the heating rate of 60 C / hour while

  to flow only from helium gas and to keep it

  held at 800 C for one hour, while flowing the gaseous mixture of He and CF4 in the same ratio of 2 liters / minute to 0.2 liter / minute. The dry gel is then heated to 900 ° C. at the rate of

   C / hour, while flowing helium ga-

  Zeux only and maintained at 900 C for one hour while flowing the gaseous mixture of He and CF4 in the ratio of flow rates of 2 liters /

  minute at 0.2 liter / minute to remove the OH group.

  Then the dry gel is brought to 1000 C at the speed of

   C / hour while flowing-the mixture

  He and O2 in the ratio of flow rates from 2 liters / minute to 0.4 liters / minute and maintained

  at 1000 C for one hour to remove fluoride.

  We still wear the dry gel at 1250 C at the speed of

   C / hour while flowing helium ga-

  zeux only and is kept at 1250 ° C

  minutes to close the pores in the gel.

  By replacing the dry gel in the oven,

  dry gel from 1250 C to 1400 C at the heating rate of 60 C / hour and maintained at 14000 C

  for 2 hours and then we obtain the trans-

parent of silica.

  The amount of OH group included in the glass

  silica is less than one part per million.

  In addition, even if the silica glass in the molten state is heated to about 20000.degree.

  of the annular heating device, it does not occur

no foaming.

  It is known that by incorporating fluoride with silica glass, the refractive index of the glass is lowered. Therefore, if the optical fiber is formed of tubular silica glass incorporating fluoride as obtained in this example and serving as a material

  sheathing, and if pure silica glass serves as the

  of heart, the cost of manufacture can be considerably reduced in comparison with an optical fiber using a heart incorporating germanium and which

  is currently used in general.

  As has been mentioned so far, by the

  Given sol-gel according to the invention, high quality tubular silica glass is provided at a low price with high dimensional accuracy. We use

  a silica glass as above as tube

  support or as a cladding tube in the

  cation of the matter-maltre for an optical fiber.

  In addition, using low refractive index silica-fiber glass incorporating fluoride as cladding material and glass

  of pure silica as the core, an optimum fiber is

  than at a lower manufacturing cost. -

  This is why the invention provides cheap optical fibers, which are expected to be requested in large quantities in the future,

Claims (34)

  1. Process for the preparation of a tubular silica glass, characterized in that it consists of:   - add silica to ultraviolet particles   fines to the sol solution obtained by hydrolyzing the metal alkoxide in an amount of 0.2 to 5 moles of silica per mole of metal alkoxide; - place the soil solution including the   ultrafine silica in a cyan container   lindrique and to gel.the soil solution by making turn the container, -   - Dry the gel to form a dry gel; - and   - vitrify the dry gel to form a green tubular silica.   2. The process of claim 1, wherein   in that the metal alcoholate is an alcohol   silicon of formula Si (OR) 4, R being a group of eg alkyl.   3. Process according to claim 1 or 2,   characterized in that the ultra-particulate silica   thin is selected from the white carbon obtained by hydrolyzing SiC14 by an oxyhydrogen torch,   the ultrafine particle silica obtained by the   wet ceded using sodium silicate as   starting material, and ultrafine silica   fine obtained by hydrolyzing the metal alcoholate by ammonia.   4. Method according to claim 1, 2 or 3, characterized in that it consists in: - dispersing uniformly, after the addi-   silica to ultrafine particles in solution.   starting soil, silica in ultrafine particles   in the soil solution by ultrasonic vibration sound.   5. Method according to one of the claims   1 to 4, characterized in that it consists in dispersing   uniformly, after addition of the silica in parti-   ultrafine molecules to the starting soil solution, the silica in the soil solution through a separator centrifugal.   6. Process according to one of the claims   1 to 5, characterized in that it consists in adjusting the pH of the soil solution between 3 and 6 by adding of a base.   7. The process of claim 5, wherein   in that the base is ammonia, ammonia, an aqueous solution of ammonia, triethylamine, an aqueous solution of triethylamine, pyridine, an aqueous solution of pyridine,   aniline, or an aqueous solution of aniline.   8. Process according to one of the claims   1 to 7, characterized in that it consists in regulating the rotation, when taking in gel by rotation, of   so that the maximum centrifugal force at   the soil solution is subjected to either 1000 g (g = 980 cm / second 2) or less than this value.   9. Process according to one of the claims   1 to 7, characterized in that it consists in gelling the soil solution in a container having a   lid covering the container and provided with   representing 50% or less of the surface of the cou- vercle.   10. Process according to one of the claims   1 to 8, characterized in that it consists in gelling the soil solution at a temperature of 5 to 60 C, then raising the temperature between 20 and 120 C at a speed   120 C / hour or lower than this value to obtain   dry gel by the drying process with contrac- tion.   11. Process according to one of the claims   1-9, characterized in that vitrification of the dry gel includes steps of (1) removing the absorbed water, (2) removing the carbon, and (3) making the non-porous dry gel. -   12. The process of claim 10 wherein   characterized in that it consists in eliminating the ab-   sorbated by at least one step of heating the dry gel to a first selected temperature of between 20 and 4000 ° C., at a speed of 400 ° C./hour or at a speed below this value and keeping the gel dry at the first chosen temperature during less an hour.   13. The process of claim 10 wherein   characterized in that it consists in removing the carbon by at least one stage of heating the dry gel to a second selected temperature of between about 400 and 11000 C, at a heating rate of between 30 and 400O C / hour and maintaining of the material at this second chosen temperature for at least 3 hours.   14. The process of claim 10 wherein   characterized in that it consists in rendering the gel non-porous dry by at least one stage of dry gel heating at a third selected temperature of between 1000 and 1400 C, at a heating rate between 30 and 400 C / hour.   15. Process for the preparation of a tubular glass   silica gel by the sol-gel process, using an alkyl silicate as the main material, characterized in that it comprises: by gelling, in the tubular form the soil consisting of a solution A comprising a solution of alkyl silicate hydrolyzed by an acid catalyst and a solution B comprising a solution of alkyl silicate hydrolyzed by a basic catalyst; - Dry the gel in a dry gel; and - vitrify the dry gel to form a transparent glass.   16. The process of claim 15, wherein   characterized in that solution B comprises parti-   silica particles whose particle diameter is   between 0.01 micron and 1.0 micron.   17. The method of claim 15 or 16, characterized in that it consists in concentrating the solution B to adjust the concentration of the 3 3   silica between 0.15 g / cm and 1.0 g / cm3 before mixing with solution A. 18. Process according to claim 15, 16 or 17, characterized in that the mixing ratio of   solution A and solution B is such that the quantity   silica content of the solution A M (A), relative to that of the solution B M (B) is between 0.2 and 3, namely M (A) / M (B) = 0.2 to 3.   19. Process according to one of the claims   at 18, characterized in that it consists in adjusting   the pH of the mixed soil solution consisting of   A and B before gel setting between 3 and 6, adjusting the pH of one or both A and B solutions   previously, or by adjusting the pH of the mixture of solu- A and B.   20. Process according to one of the claims   at 19, characterized in that it consists of pouring the soil into a cylindrical container and to gel it in rotating this container.   21. The process of claim 20, wherein   characterized in that it consists in adjusting the speed of   rotation, when rotating in gel, of   the maximum centrifugal force acting on the ground is 1000 g (g = 980 cm / second2) or less than this value.   22. Process according to one of the claims   21, characterized in that it consists, when   the wet gel is dried, covering both ends.   of the cylindrical container of lids having apertures representing 10% or less of the area   of the lid, the moist gel being dried in the container cylindrical pill.   23. Process according to one of the claims   at 22, characterized in that it consists, when drying the wet gel, to remove the wet gel from the cylindrical container and to place it in a second container having openings representing 10% or less of the surface of this second container, the gel   wet being dried in the second container.   24. Process according to one of the claims   at 23, characterized in that it consists of gelling the soil at a temperature between 5 and 60 C, then raising the temperature between 40 and 150 C, at a heating rate of 120 C / hour or at a speed below this value to get the dry gel by   the drying process with contraction.   25. Process according to one of the claims   15 to 24, characterized in that the vitrification of the dry gel comprises the stages of (1) elimination of   water absorbed, (2) carbon removal, (3)   to accelerate the condensation reaction with dehydration, (4) - closing the pores of the dry gel and (5) converting the dry gel into a clear glass.   26. Process according to one of the claims   at 24, characterized in that the vitrification of the dry gel comprises the stages of (1) removal of absorbed water, (2) removal of carbon, (3)   treatment to accelerate the condensation reaction.   dehydration, (4) removal of OH groups, (5) removal of chlorides or removal of fluorides, (6) pore closure of dry gel and   (7) transformation of the dry gel into a clear glass.   27. Preparation process according to the   25 or 26, characterized in that it consists in eliminating the water absorbed from the dry gel by at least one   stage of heating the dry gel at a first temperature   chosen between 20 and 4000 C at the speed   heating of 400O C / hour or at a lower speed than   re at this value, and keeping this gel dry at this first chosen temperature for at least one o'clock.   28. Process according to one of the claims   at 27, characterized in that it consists in removing the carbon by at least one stage of heating the dry gel to a second selected temperature of between 400 and 9000 C at the heating rate of 30 to 4000C / hour.   29. Process according to one of the claims   28, characterized in that it consists in accelerating   Rer the condensation reaction with dehydration of the dry gel by at least one stage of heating the dry gel to a third selected temperature between 900 and 1200 C at the heating rate of 30 to 400 C / hour and maintaining the dry gel at this third temperature chosen for at least 30 minutes.   30. Process according to one of the claims   26 to 29, characterized in that it consists in eliminating the OH group by flowing the gas chosen from gas consisting of helium gas, oxygen gas, nitrogen gas, argon gas and gaseous gas mixture. helium, oxygen, nitrogen and argon, and the OH group removal agent in a quantity   representing 1 to 40 x with respect to the gas in the.   oven at a temperature chosen between 700 and 1100 C.   31. Process according to claim 16, characterized in that the agent eliminating the OH group   is Cl2, SOCl2, SF6, CF4, C2F6 or C3F8.   32. Process according to one of the claims   26 to 31, characterized in that it consists, after removing the OH group, in removing chlorides or fluorides by flowing gas selected from helium gas, argon gas, nitrogen gas and the gaseous mixture of helium, argon, nitrogen and oxygen, in an amount representing from 1 to 100%   gas in the oven at a temperature chosen between 800 and 1200 C.   33. Process according to one of the claims   at 32, characterized in that it consists in rendering the gel non-porous dry by at least one drying stage   frost, while putting the oven under vacuum or   circulating helium gas, at a fourth temperature selected between 900 and 1350 C at the heating rate of 30 to 400O C / hour and maintaining the   dry gel at this fourth selected temperature, at least one hour.   34. Process according to one of the claims   at 33, characterized in that it consists, after rendering the gel non-porous dry, to transform it into   clear glass by heating it to a fifth temperature   selected ture between 1200 and 1600 C, and maintaining the dry gel at this fifth temperature chosen.